Mechanics of Respiration - Quiz 2 Flashcards
Goals of Respiration
- Distribute air and blood flow for gas exchange
- Provide oxygen to cells
- Remove CO2
- Maintain constant homeostasis for metabolic needs
Functions of Respiration
- Mechanics of Pulmonary Ventilation
- Diffusion of O2 and CO2 b/t alveoli and blood
- Transport O2 and CO2 to and from tissues
- Regulation of ventilation & respiration
External Respiration
Mechanics of breathing
Movement of gases in and out of body
Gas transfer from lungs to tissues of body
Maintain body & cellular homeostasis
Internal Respiration
Intracellular oxygen metabolism
Cellular transformation
Kreb cycle - aerobic ATP generation
Mitochondria and O2 utlization
What is primary purpose of Ventilation?
Maintain an optimal composition of alveolar gas
What acts as a stabilizing buffer compartment between the environment and pulmonary capillary blood?
Alveolar gas
- O2 constanstly removed from alveolar gas by blood
- CO2 continuously added to alveoli from blood
- O2 replenished and CO2 removed by ventilation, by simple diffusion
What provides the stable alveolar environment?
The Two Phases of Ventilation
Weight of the Lungs
1.5% of Body Weight
1 kg in a 70 kg adult
60% of lung weight is Alveolar tissue
Alveoli have a very ________ surface area
Large
70 m2 internal surface area
40 times the external body surface area
Gas Diffusion Pathway
Short Pathway
Permits rapid and efficient gas exchange
1.5 µm b/t air and alveolar capillary RBC
What is the volume of blood in the Lung
500 mL
(10% of TBV)
Factors Needed to Alter Lung Volumes
- Respiratory muscle generate force to inflate/deflate lungs
- Tissue elastance and resistance impedes ventilation
- Distribution of air movement in lung, resistance in airway
- Overcoming alveolar surface tension
Breathing Cycle
- Airflow needs pressure gradient
- Air flows from higher to lower pressure
- Inspiration: alveolar pressure < atmostpheric, allows airflow into lungs
- Expiration: Alveolar pressure > atmospheric, allows airflow out of lung
Inspiration
Active Phase of Breathing
- Motor signals from brainstem activate muscle contraction
- Phrenic Nerve (C3, C4, C5) transmits motor stimulation to diaphragm
- Intercostal Nerves (T1-T11) send signals to external intercostal muscles
- Thoracic cavity expands to lower pleural space pressure
- Pressure in alveloar ducts & alveoli decreases
- Fresh air flows in until pressures are equalized
- Inhaling is negative-pressure ventilation
Changes in alveolar pressure is generated by what?
Changes in pleural pressure
Most important muscle of Inspiration
Diaphragm
- 75% of inspiratory effort
- Thin, dome-shaped muscle on lower ribs, xiphoid process, lumbar vertebra
- Innervated by Phrenic Nerve (C 3, 4, 5)
What happens during diaphragm contraction?
- Abdominal contents forced downward and forward causing increase in vertical dimension of chest cavity
- Rib margins lift and moved outward causing increase in transverse diameter or thorax
- Diaphragm moves down 1 cm during normal inspiration
- During fored inspiration, diphragm can move down 10 cm
Paradoxical Movement of Paralyzed Diaphragm
Upward movement with inspiratory drop of intrathoracic pressure
Occurs when diaphragm muscle is denervated
Transdiaphragmatic Pressure
- Abdominal pressure effects entire diaphragm
- Abdominal pressure is equal to atm. pressure in supine position when respiratory muscles are relaxed
- Increasing abdominal pressure pushes diaphragm up into thoracic cavity, decreasing FRC
(Functional Residual Capacity)
What reduces Functional Residual Capacity (FRC)?
Intra-abdominal pressure
EX: Pregnancy, obesity, SBO, lap. surgery, ascites, abdominal mass, hepatomegaly, Trendelenburg, valsalva maneuver
How are External Intercostal Muscles (EIM) innervated?
- 25% Inspiratory effort
- Connects to adjacent ribs
- Motor neurons from respiratory brainstem go down spinal cord and leaves spinal cord via the intercostal nerves.
- Then they go to chest wall under each rib along with the intercostal veins and arteries.
- Contraction of EIM pulls ribs upward and forward
What happens when the External Intercostal Muscles (EIM) contract?
- Thorax diameters increase in both lateral and anteroposterior directions
- Ribs move outward in “bucket-handle” fashion
- Intercostal nerves from spinal cord roots innervate EIMs
What happens if the External Intercostal Muscles (EIM) are paralyzed?
Not much. Paralysis of EIM does not really alter inspriations because the diaphragm is so effective, but sensation of inhalation decreases.
Accessory Muscles
Inspiration Muscle
Assist with forced inspiration during stress/excercise
- Scalene Muscle
- Sternocleidomastoid Muscle
Scalene Muscle
Accessory Muscle that attach cervical spine to apical rib
Elevate first two ribs during forced inspiration
Sternocleidomastoid Muscle
Accessory muscle that attach base of skull (mastoid process) to top of sternum and clavical medially
Raise the sternum during forced inspiration
Expiration
Passive Phase of Breathing
- Chest muscle and diaphragm relax contraction
- Elastic recoil of thorax and lungs return to equilibrium
- Pleural and alveolar pressure rise
- Gas flows passively out of lung
- Active expiration during hyperventilation and exercise
What is needed for Active Expiration
Abdominal and Internal Intercostal Muscle Contraction
- Rectus abdominus/abdominal oblique muscles
- contraction raises intra-abdominal pressure to move diaphragm up
- intra-thoracis pressure raises and forces air out lungs
- Internal Intercostal Muscles
- assist expiration by pullin ribs down and in
- decrease thoracic volume
- stiffen intercostal spaces to precent outward bulging
- These muscles also contract forcefully during coughing, vomiting, and defecation
What is Transpulmonary Pressure?
Pressure difference between the alveolar pressure and pleural pressure on the outside of the lung
What do the alveoli tend to do when the pleural pressure tries to pull outward?
Collapse together
Even more profound in chlidren. PEEP is your best friend.
What is Recoil Pressure
Elastic forces that tend to collapse the lung during respiration
What are the parts of the pleural membrane?
Visceral Pleura
Thin serosal membrane that covers the lobes of the lungs
Parietal Pleura
Lines the inner surface of chest wall, lateral mediastinum, and most of diaphragm
- These two slide against each other and are hard to separate.
- Separated by thin layer of serous fluid (a lot would be p. effusion)
- EX: CHF, Cancer
What do the visceral pleura and parietal pleura form when they fold inferiorly?
Pleura Sac
Both pleura lines this space enclosing a small amount of fluid
What is Pleural Fluid?
- Lubricant between the membranes, prevents frictional irriation
- Makes visceral and parietal membrane stick together, maintains surface tension
- Lymphatic drainage maintains constant suction on pleura (-5cmH2O)
Pleural Pressure
- Pressure of fluid in space between pleura membranes - always negative (-5cmH2O)
- At rest, suction creates negative pressure at start of inspiration (-5cmH2O) - holds lungs open
- Pressure get more negative during inspiration (-7.5 cmH2O) allowing for negative-pressure inspiration
- Lung Collapse with Positive Pleural Pressure: Pneumothorax, Hemothorax, Chlythorax
Tidal Volume (TV)
Volume of air moved in/out of lung during breathing
Total Lung Capacity (TLC)
Volume in the lungs at max inflation
TLC = IRV + ERV + RV + TV
TLC = 5.5 L
Inspiratory Reserve Volume (IRV)
Max volume that can be inhaled from the end-inspiratory level
IRV = 2.5 L
Expiratory Reserve Volume (ERV)
Max volume of air that can be exhaled from end-expiratory position
ERV = 1.5 L
Residual Volume (RV)
Volume of air remaining in lungs after maximal exhalation
RV = 1 L
Vital Capacity (VC)
Volume breathed out after deepest inhalation
VC = IRV + TV + ERV
VC = 4.5L
Functional Residual Capacity (FRC)
Volume in lungs at end-expiratory position
FRC = ERV + RV
FRC = 2.5 L
Spirometry
- 4 Volumes - Based on Ideal Body Weight
- IRV = 2.5 L
- ERV = 1.5 L
- RV = 1 L
- TV = 0.5 L
- 4 Capacities
- VC = 4.5 L
- IC = 3 L
- FRC = 2.5 L
- TLC = 5.5 L
- Effort Dependent
- Values vary to height, age, sex & physical training
Lung Capacities
A capacity is always a sum of certain lung volumes
TLC = IRV + TV + ERV + RV
VC = IRV = TV + ERV
FRC = ERV + RV
IC = TV + IRV
Lung Compliance
- Measure of distensibility of lungs
- Compliance = Change in Lung Volume / Change in Lung Pressure
- Cpulm = ΔVpulm / ΔPpulm
What is the extent of lung expansion dependent on?
Increase of transpulmonary pressure
Normal static lung compliance
70 - 100 mL of air / cm H2O transpulmonary pressure
Different compliances for inspiration and expiration based on the _________ of lungs
Elastic forces
What REDUCES lung compliance
Higher or Lower Lung Volumes
Higher expansion pressures
Venous Congestion
Alveolar Edema
Atelectasis and FIbrosis
What INCREASES lung compliance
Increased Age
Emphysema secondary to alterations of elastic fibers
Pressure-Volume Curve: Hysteresis
- Inflation and deflation curves differ
- Lung volume during deflation is larger than during inflation
- Trapped gas in closed small airways cause higher lung volumes
- Increased age and lung disease have more small airway closure
What are elastic lung tissue made of and its natural state
Elastin and Collagen fibers of the lung - natrual state is contracted coils
How is elastic force generated?
Return of coiled state after being stretched and elongated
Recoil force helps deflate lungs
Surface Air-Fluid Interface
2/3 of Total elastic force in lung
Surface tension of H2O
What holds alveoli open?
Complex syngery between air and fluid
Surfactant reduces surface tension and keep alveoli from collapse
DPPC - Dipalmitoyl Phosphatidyl Choline
Main constituent of surfactant
Hydrophobic and Hydrophilic ends
Opposes water self-attraction and reduces surface tension
Alignment of Repulsive Forces
Reduction of surface tension greater when film compressed closer as DPPC repel each other more
Functions of Surfactant
- Lowers surface tension of alveoli and lung
- increase compliance, decrease work of breathing
- Promotes stability of alveoli - prevent collapse and helps parenchyma
- 300 million tiny alveoli tend to collapse
- Prevents drawing of fluid into alveoli from capillaries
Total Ventilation/ Minute Ventilation
Total volume of air into lungs per minute
Minute ventilation = Tidal Volume x Frequency
Average 6L/min = 500 cc x 12 breaths/min
Alveolar Ventilation
70% of minute ventilation due to (30% dead space)
Alveolar O2 concentration is steady when supply = demand
VT = VA + VD
Wasted Ventilation
- Anatomical dead space and any portion of alveoli that does not exchange gas
- Physiologic Dead Sace - deviation from ideal ventilation related to blood flow
- Ventilation/blood flow (V/Q) mismatch when blood flow is blocked - emboli
Airway Closure
- Base of lung has gas trapped and cant breathe out CO2 with every breath
- defective gas exchange in dependent (down) regions (intermittently ventilated)
- Closing Volume (volume of closed small airways)
- CV > FRC leads to atelectases and hypoxemia
- In patients with chronic lung disease
Bernoulli Effect
As speed of fluid increases, pressure exerted by fluid decreaases
Airflow through Tubes
Low flow rates = laminar/constant/parallel streams
High flow rates = turbulence
(Airway branches/diameter, velocity/direction changes)
Flow velocity in a tube in Laminar Flow
Velocity in center of tube/airway is twice as fast than at the edges
Poiseuille Law
Describes resistance to flow through a tube
- Pressure increases proportional to flow rate & gas viscocity
- Small airway radius and longer distances increase flow resistance
- R = (8 x L x n) / (π x r4) *R: resistance, L: length, n: viscosity, r: radius
- Reducing r by 16% will double R
- Reducing r by 50% will increase R by 16x
Ohm’s Law
P = F x R
*P: Pressure, F: FLow, R: resistance*
What happens during turbulent flow?
- Local eddies form at sides of airway and flow gets disorganized
- Pressure no longer proportional to flow
- More density, velocity, and airway resistance = more turbulence
Chief Site of Airway Resistance
Major resistance at medium-sized bronchi
- Most of pressure drops at seventh division
- Very small bronchioles have very little resistance
- < 20% drop at airways < 2mm
- Parardox due to large number of small airways
- Air speed gets low, difffusion takes over
Factors of Airway Resistance
- Lung Volume - as lung vol. reduced, resistance increases
- Bronchial Smooth Muscle
- Airway contraction = increased resistance
- Density and Viscosity of Inspired Gas
- Density has greater effect on resistance
Less space = more resistance
Work of Breathing
- Work = Pressure X Volume (W = PxV)
- Oxygen consumption used to determine work of breathing
What is the O2 cost of breathing?
5% of total resting oxygen consumption
30% for hyperventilation
High cost in COPD limits exercise ability
What position decreases abdominal pressure and allow for easier lung ventilation?
Upright, Reverse Trendelendburg, & Prone
What can FRC and TLC be determined by?
- Helium dilution
- Nitrogen washout
- Body plethysmography
What CANT Spirometry measure?
CANT measure Residual Volume, meaning FRC and TLC cant be determined using spirometry alone
What happens to TLC, RV, and PEFR in Obstructive Lung Disease?
TLC: Increases
RV: Increases
PEFR: Decreases
Coving of Expiratory Curve
What happens TLC, RV, and PEFR in Restrictive Lung Disease?
Restrictive - shifts to the Right
TLC: Decreases
RV: Decreases
PEFR: Decreases
Decreased Inspiratory Flow
No Coving
What happens to TLC, RV, PEFR in Fixed Upper Airway Obstruction (Tracheal Stenosis, Tumor, Goiter)
RV: Increased
PEFR/PIFR: Decreased
